Step down gear train, more specifically for an adjusting device of an automotive vehicle seat

ABSTRACT

“A step down gear train is provided including an output shaft that rotates about an output axis, a housing that is rotatable relative to the output shaft, a toothed washer having a circumferential first toothed surface, an eccentric that is rotatably disposed on said output shaft and has an eccentric driving surface which is offset relative to the output axis by an eccentricity, the eccentric comprising a driving region, an annular gear comprising a circumferential second toothed surface, a circumferential third toothed surface and an eccentric driven surface cooperating with the driving surface, a gearwheel comprising a circumferential fourth toothed surface, said first toothed surface of the toothed washer and said second toothed surface of the annular gear meshing together in a first angular position and forming a first nutating gear having the eccentricity and the third toothed surface of the annular gear and the fourth toothed surface of the gearwheel meshing together in a second angular position that is offset by 180 degrees relative to the first angular position with respect to the output axis and forming a second nutating gear also having the eccentricity.”

The invention relates to a step down gear train that is particularlysuited for use in an adjusting device of an automotive vehicle seat. Asis well known, it has an output shaft which rotates about an outputaxis. A housing accommodates the various gear parts, the output shaft isrotatable relative to the housing. Two eccentric gear stages areprovided, a first eccentric gear stage having a toothed washer withcircumferential teeth meshing with the teeth of an annular gear. Asecond eccentric gear stage is formed by the annular gear and by agearwheel comprising circumferential teeth. The annular gear is providedwith an eccentric driven surface that cooperates with a mating drivingsurface. The two nutating gear stages have the same eccentricity e.

Such type step down gear trains are widely used in adjusting devices forautomotive vehicle seats. They have proved efficient. They have a quitehigh gear reduction ratio, which is particularly advantageous for stepdown gear trains that are driven by means of an electric motor. Thereader is referred to U.S. Pat. No. 6,543,850 B1 for an example of priorart.

A problem with step down gear trains of this type is to achievemanufacturing accuracy and zero clearance. Step down gear trains areoften utilized for adjusting devices in which minimal clearance is to beprovided in spite of the longer lever arms formed by the one and/or theother of the parts to be adjusted. An adjusting device for theinclination of the backrest will be taken as an example. Here, thebackrest forms a quite long lever. An adjusting device disposed in theregion of the axis of the backrest should have no play that could benoticed at the upper edge of the backrest.

Another problem lies in providing proper meshing of the teeth of the twonutating gear stages. According to prior art, the annular gear hascommon teeth that mesh with both the toothed washer and the gearwheel.The result thereof however is that the teeth of the paired teeth of atleast one of the two nutating gear stages cannot be configuredoptimally.

In view thereof, it is the object of the invention to indicate a stepdown gear train that allows an optimal geometry of the teeth to beachieved and that preferably has a low overall height in the axialdirection.

This object is solved by a step down gear train having the features ofpatent claim 1.

The two nutating gear stages engage in angular positions that are offsetby 180 degrees. This permits to keep low the tilt moments exerted byeach nutating gear stage onto the output axis, in the best case to evenreduce them to almost zero.

The two nutating gear stages may each be optimally adapted to eachother. As opposed to prior art, the first toothed surface of the toothedwasher can be formed to accurately mate the second toothed surface ofthe annular gear without having to take the other toothed surfaces intoconsideration. The same applies to the third toothed surface of theannular gear and to the fourth toothed surface, which again may be madeso as to optimally match together without having to take the othertoothed surfaces into consideration. As a result, the two nutating gearstages can be configured optimally with regard to their meshingfeatures.

In a preferred developed implementation, the second toothed surface andthe third toothed surface of the annular gear are of a different typewith the second toothed surface being an externally-toothed surface andthe third toothed surface an internally-toothed surface or conversely,the second toothed surface being an internally-toothed surface and thethird toothed surface an externally-toothed surface. This configurationpermits to arrange all the toothed surfaces in one radial plane. Theresulting overall height is low and the tilt forces exerted onto theoutput shaft are small.

In order to achieve the highest possible gear reduction ratio, thedifference in the number of teeth between the first toothed surface andthe fourth toothed surface should advantageously be as small aspossible. It has proved particularly advantageous to configure anutating gear stage in such a manner that the two toothed surfacesinvolved have the same number of teeth. In this case, this gear stagedoes not participate in reducing the gear, it merely has ananti-nutating effect, meaning it accommodates the wobbling motion of theother nutating gear stage. Gear reduction is achieved with only theother nutating gear stage, which is configured accordingly.Advantageously, the number of teeth differs by one tooth between the twotoothed surfaces.

In a preferred developed implementation, the housing has a housing partand the toothed washer or the gearwheel is integrally connected to saidhousing part or is formed by said housing part. This permits toeconomize on a separate component part and the gear train is of shortconstruction in the axial direction.

A more advantageous implementation is achieved if the two toothedsurfaces of the annular gear have the smallest possible toothdifference, more specifically only a one-tooth difference and preferablyno tooth difference at all. This makes it possible to configure theannular gear in such a manner that at each tooth the wall thickness ofthe annular gear is substantially the same as that of any other randomlychosen tooth. Accordingly, the annular gear has a stability that doesnot substantially vary with the angle of rotation.

In another preferred embodiment, the output shaft has a pinion that isconnected thereto. In practical use, said pinion engages one of the twoparts of the automotive vehicle seat that are to be adjusted relative toeach other.

In another improvement, there is provided a driver member that isconnected to the output shaft. The gearwheel has a driver surface forcooperation with said driver member and for providing a non-rotatable,releasable connection between the driver member and the gearwheel. Thispermits easy mounting of the gear train. It is advantageous to combinethe driver member with the pinion, for example to form the driver memberin an end region of the pinion.

Other features and advantages will become more apparent upon reviewingthe appended claims and the following non restrictive description ofembodiments of the invention, given by way of example only withreference to the drawing. In said drawing:

FIG. 1: is a perspective illustration in the form of an assembly drawingshowing a first embodiment, a pinion being shown at the front,

FIG. 2: is an illustration like FIG. 1, but now turned into anotherviewing direction, the pinion is now at the back,

FIG. 3: is a top view of an assembled gear train, but without a wormwheel, the viewing direction being similar to that in FIG. 2,

FIG. 4: is an axial sectional view of the assembled gear train,

FIG. 5: is an axial sectional view of a gear train similar to that inFIG. 4 in a second embodiment and

FIG. 6 is an axial sectional view of a gear train in a third embodimentand similar to FIG. 4, the drive being now configured as a handwheel.

Herein after, the first embodiment as shown in the FIGS. 1 through 4will be first described. The explanations given in this context howeveralso apply to the other exemplary embodiments so that the otherexemplary embodiments are not further described except insofar as theydiffer from the first exemplary embodiment.

The step down gear train has an output shaft 20 that extends through theentire gear train, as best shown in FIG. 4. It serves to carry severalcomponent parts. It rotates about an output axis 22. There is furtherprovided a housing, with only one housing part 24 being shown in therespective one of the FIGS. The output shaft 20 rotates relative to saidhousing part 24, the output axis 22 is stationary relative to thehousing part 24. A toothed washer 26 is configured integral with saidhousing part 24, it has a circumferential internally-toothed surface,the toothed surface of the toothed washer 26 will be referred to asfirst toothed surface 28 herein after. The housing part 24 is asubstantially flat component part, it can be manufactured by anembossing or a stamping technique or by any other suited process. Thefirst toothed surface 28 is pressed, stamped or manufactured in anotherway from the material of the housing part 24.

A second toothed surface 30, which is implemented as anexternally-toothed surface, meshes with the toothed washer 26. It isformed on an annular gear 32 which has still another toothed surface,namely the third toothed surface 34. The first toothed surface 28 andthe second toothed surface 30 form a first nutating gear stage or aneccentric gear. As is well known, a nutating gear stage consists of twotoothed surfaces, an internally-toothed surface and anexternally-toothed surface. On the externally-toothed surface, the tipsof the teeth lie on a circle that is smaller by at least one toothheight than the circle on which lie the tips of the teeth of theinternally-toothed surface. The centers of the two toothed surfaces 28,30 are offset by an offset dimension or eccentricity e.

The two toothed surfaces 28, 30 are formed to accurately mate andpreferably have involute form gear teeth. A fourth toothed surface 36meshes with the third toothed surface 34 of the annular gear 32, it isformed as an externally toothed surface on a gearwheel 38. Saidgearwheel 38 is located between the housing part 24 and the annular gear32. The third toothed surface 34 and the fourth toothed surface 36 forma second nutating gear stage. The toothed surfaces of this secondnutating gear stage are also optimally adapted to each other. Theeccentricity e of this nutating gear stage equals the eccentricity ofthe first nutating gear stage. However, meshing of the toothed surfaces28, 30 of the first nutating gear stage occurs, with respect to theoutput axis 22, offset by 180 degrees relative to the meshing of thesecond nutating gear stage consisting of the third toothed surface 34and the fourth toothed surface 36. This is shown in FIG. 3. There, itcan be seen that the first nutating gear stage meshes at the twelveo'clock position, whereas the second nutating gear stage meshes at thesix o'clock position. As a result, the forces the two nutating gearstages exert onto the output shaft 20 are directed in opposingdirections. Since the two toothed surfaces are located in the sameplane, these forces almost counterbalance each other. Accordingly, thetilt load on the output shaft 20 is small.

With regard to the number of teeth of the two nutating gear stages, thefollowing applies: in the exemplary embodiment shown, the toothed washer26 has minus 20 teeth, minus designating the internally-toothed surface.The associated second toothed surface 30 has plus 19 teeth, with plusreferring to the externally-toothed surface. The third toothed surface34 formed on the same annular gear 32 has minus 19 teeth, the associatedfourth toothed surface 36 has plus 18 teeth. Accordingly, the firsttoothed surface 28 and the fourth toothed surface 36 differ by twoteeth.

It is particularly advantageous to configure one of the two nutatinggear stages in such a manner that the two toothed surfaces of thisnutating gear stage have the same effective number of teeth, meaningthat they are composed of a gear pair minus 20 and plus 20. Such anutating gear stage does not participate in reducing the gear, it merelyserves to suppress the nutating motion. If such a nutating gear stage isprovided, the other nutating stage must effect the transmission, it maythen be configured in such a manner that the tooth difference is one.This permits to achieve the highest possible gear reduction ratio.

The housing part 24 has a bearing hole 40 that is centered on the outputaxis 22. A bearing shoulder 42 of the gearwheel 38 is formed so as toconform thereto. Thus, the gearwheel 38 is carried in the housing part24 so as to be rotatable about the output axis 22. As shown in FIG. 4,the gearwheel 38 directly contacts the neighboring surface of thehousing part 24 in the region of its fourth toothed surface 36. Thetooth depth of all of the toothed surfaces 28, 30, 34, 36, as measuredin the axial direction, is substantially the same. As a result, thegearwheel 38 is located within the recess formed by the first toothedsurface 28 formed in housing part 24. The second toothed surface 30 andthe third toothed surface 34 are also located in the region of saidrecess. All of the toothed surfaces 28, 30; 34, 36 lie in one plane.

The two toothed surfaces 30 and 34 of the annular gear 32 have the samenumber of teeth. As a result, the material thickness of the annular gear32 as viewed in revolution only varies with the gear period and notadditionally as this would be the case if the two toothed surfaces 30,34 had differing numbers of teeth for example. In that these toothedsurfaces 30, 34 have the same number of teeth, constant stability may beachieved for the annular gear 32 independent of the angle about theoutput axis 22.

A pinion 44 is connected fixedly to the output shaft 20. It protrudes onthe side of the housing part 24 that opposes the toothed surfaces 28,30; 32, 34 and that is located on the outside when assembly of the geartrain is completed.

One end of the pinion 44, which is turned toward the toothed surfaces,is lathed or stepped in another way, thus forming a driver member 46.Said driver member can also be configured in another shape and otherwiseconnected to the output shaft 20. A driver surface 48 configured in thegearwheel 38 corresponds to the driver member 46. As the driver member46 engages with the driver surface 48, the gearwheel 38 is non-rotatablylinked to the output shaft 20 but is releasable in the axial direction.

The gear train has an eccentric 50 comprising an internal hole by whichit is carried so as to be rotatable about the output axis 20. It has aneccentric driving surface 52 having the eccentricity e. The annular gear32 has an accordingly configured eccentric driven surface 54 of aneccentricity e. Cooperation of the two surfaces 52, 54 effects nutatingmotion of the two nutating gear stages. When the eccentric 50 isrotated, the angular positions in which the respective ones of the gearstages are meshing, revolve. They always remain offset by 180 degrees.Starting for example from the position as shown in FIG. 3, revolutionoccurs upon rotation of the eccentric 50. The first nutating gear stage,which meshes in the angular position corresponding to 12 o'clock, leavesfor example this position and moves toward 1 o'clock. Likewise, thesecond gear stage, which meshes in the six o'clock position, leaves thisposition and moves toward 7 o'clock.

The eccentric 50 can be manually or motor driven or driven in any otherway. In the exemplary embodiment shown, the drive occurs so as to besuited for motorized adjustment. For this purpose, the eccentric 50 isintegrally connected to a driver wheel 56 that is disposed axiallyrelative to the eccentric 50 in a direction opposing the housing part 24and/or the toothed surfaces. The driver wheel 56 is a worm wheel. Itengages a worm 58. The rotational axis of said worm 58 is stationaryrelative to the housing part 24.

As best shown in FIG. 4, the gear train is of a quite shortconstruction. The gear parts are located between the driver wheel 56 andthe housing part 24. The corresponding axial dimension is substantiallydetermined by the axial height of the toothed surfaces and by the axialdimension of the eccentric 50. It is possible to dispose the eccentricon the same plane as the toothed surfaces. The two exemplary embodimentsaccording to the FIGS. 5 and 6 go along these lines.

In the exemplary embodiment according to FIG. 5, it is not the toothedwasher 26 that is associated with the housing part 24, here it is ratherthe gearwheel 38 that is formed by the housing part 24. As a result,only the toothed washer 26 and the gearwheel 38 substantiallyinterchange their functions. Now, it is the toothed washer 26 that isnon-rotatably linked to the output shaft 26 for which purpose the driversurface 48 is now provided on the toothed washer 26.

With this embodiment as well, the interaction between the drivingsurface 52 of the eccentric 50 and the associated driven surface 54 onthe annular gear 32 now occurs in the reverse direction. The drivensurface 54 now is a surface formed on the outer periphery of the annulargear 32 with the driving surface 52 accordingly being a surface opposingthe output shaft 20.

The embodiment according to FIG. 6 differs in an important aspect fromthe previous exemplary embodiments: the eccentric 50 is now driven by ahandwheel 60. No gear train is interposed, the eccentric is drivendirectly. Like in the first exemplary embodiment, the driving surface 52of the eccentric 50 is a surface that lies radially outside.Accordingly, the driven surface 54 of the annular gear 32 is a radiallyinternal surface. In this exemplary embodiment, the two toothed surfaces30 and 34 of the annular gear 32 have the same number of teeth. Thefirst toothed surface 28, which in turn is integrally associated withthe housing part 24, also has the same number of teeth. As a result,gear reduction only occurs in the second nutating gear stage, the thirdtoothed surface 34 and the fourth toothed surface 36 having only aone-tooth difference. The handwheel 60 is carried so as to be rotatableabout the output shaft 20. A benefit of the construction becomesapparent here. It is possible to configure the output shaft 20 so as tobe continuous and to moreover mount important parts of the gear trainthereon. As a result, both these parts and the output shaft 20 aresupported. Another benefit is that it is possible to provide connectionto another seat side on which a similar gear train can be disposed.

1. A step down gear train, more specifically for an adjusting device ofan automotive vehicle seat, comprising: an output shaft that rotatesabout an output axis, a housing that is rotatable relative to the outputshaft, a toothed washer having a circumferential first toothed surface,an eccentric that is rotatably disposed on said output shaft, and has aneccentric driving surface which is offset relative to the output axis byan eccentricity, the eccentric comprising a driving region, an annulargear comprising a circumferential second toothed surface, acircumferential third toothed surface and an eccentric driven surfacecooperating with the driving surface, a gearwheel comprising acircumferential fourth toothed surface, said first toothed surface ofthe toothed washer and said second toothed surface of the annular gearmeshing together in a first angular position and forming a firstnutating gear having the eccentricity and the third toothed surface ofthe annular gear and the fourth toothed surface of the gearwheel meshingtogether in a second angular position that is offset by 180 degreesrelative to the first angular position with respect to the output axisand forming a second nutating gear also having the eccentricity.
 2. Thestep down gear train according to claim 1, wherein the second toothedsurface of the annular gear is an externally-toothed surface and thethird toothed surface of the annular gear is an internally-toothedsurface or, conversely, the second toothed surface of the annular gearis an internally-toothed surface and the third toothed surface of theannular gear is an externally-toothed surface.
 3. The step down geartrain according to claim 1, wherein the housing has a housing part andthe housing part forms either the toothed washer or the gearwheel. 4.The step down gear train according to claim 1, wherein the secondtoothed surface of the annular gear and the third toothed surface (34)of the annular gear each have a smallest possible tooth difference. 5.The step down gear train according to claim 1, wherein the gearwheelcomprises a bearing shoulder and the housing comprises a housing partthat forms a bearing hole for said bearing shoulder.
 6. The step downgear train according to claim 1, wherein there is provided a drivermember that is connected to the output shaft and a driver surface isformed in the gearwheel for cooperation with said driver member and forproviding a non-rotatable, releasable connection between the drivermember and the gearwheel.
 7. The step down gear train according to claim1, wherein the driving region of the eccentric is configured to be aworm wheel and there is provided a worm that meshes with said wormwheel.
 8. The step down gear train according to claim 1, wherein thedriving region is configured to be a handwheel.
 9. The step down geartrain according to claim 1, wherein the first through fourth toothedsurfaces lie in one common radial plane.
 10. The step down gear trainaccording to claim 1, wherein the first toothed surface and the fourthtoothed surface have a smallest possible difference between theirrespective numbers of teeth.
 11. The step down gear train according toclaim 6, wherein there is provided a pinion that is connected.
 12. Thestep down gear train according to claim 1, wherein the eccentric drivingsurface of the eccentric is located, as viewed in an axial direction, inimmediate proximity to the second toothed surface and to the thirdtoothed surface of the annular gear and is offset in the axial directionrelative to said two toothed surfaces by as small a distance aspossible.
 13. The step down gear train according to claim 1, whereineither the two toothed surfaces of the first nutating gear or the twotoothed surfaces of the second nutating gear have a same number ofteeth.
 14. The step down gear train according to claim 1, wherein thesecond toothed surface and the third toothed surface are configureddifferently.
 15. The step down gear train according to claim 1, whereinthe first toothed surface and the second toothed surface aregeometrically optimally matched together, and have involute form gearteeth.
 16. The step down gear train according to claim 1, wherein thethird toothed surface and the fourth toothed surface are geometricallyoptimally matched together, and have involute form gear teeth.
 17. Thestep down gear train according to claim 1, wherein the second and thirdtoothed surfaces differ by at most one tooth.
 18. The step down geartrain according to claim 1, wherein the first and fourth toothedsurfaces differ by at most two teeth.